1. Field
Embodiments of the present invention relate to a disc brake which may improve restoration of a piston which occurs when braking operation is terminated.
2. Description of the Related Art
A disc brake is a device that is generally used to slow a vehicle to a stop by forcibly pressing friction pads against both sides of a disc rotating together with a wheel of the vehicle.
To reduce brake drag that is caused by continuous contact between the disc and the friction pads after the brake pedal is released, two solutions may be considered for such disc brakes. One solution is to retract the piston by using a seal and a roll-back chamfer. The other solution is to retract the piston using a compression spring for pad plates, which are pressed against the disc.
FIG. 1 is a cross-sectional view illustrating a conventional disc brake, and FIG. 2 is a view showing the piston retracted by using a seal and a roll-back chamfer.
As shown in FIGS. 1 and 2, a disc brake 10 includes a pair of pad plates 11 to generate braking force by being pressed against a disc D, a carrier (not shown) to support the pair of pad plates 11, a caliper housing 20 installed at the carrier and provided with a piston 22 slidably installed in a cylinder 21 to apply pressure to the pair of pad plates 11, and a seal interposed between an inner surface of the cylinder 21 and an outer surface of the piston 22 of the caliper housing 20. The seal 30 serves to seal the space between the inner surface of the cylinder 21 and the outer surface of the piston 22 to ensure that brake oil does not escape and to allow the piston 22 to be moved forward in the direction of arrow A, as shown in FIG. 2, for implementation of braking and moved back to an original position thereof by resilience of the seal 30, by which the seal 30 recovers an original shape thereof, when the braking pressure is released.
The seal 30 is formed in a shape of a ring to be inserted into a circular roll-back chamfer 23 provided in the inner surface of the cylinder 21, and has a quadrilateral cross section. In addition, the roll-back chamfer 23 to accommodate the seal 30 is provided with a slope 24 at a portion of its opening facing the direction opposite to the direction (arrow A) in which braking is performed to allow the seal 30 to be deformed when the piston 22 is moved forward in the direction of braking, as shown in FIG. 2.
When the piston 22 is moved forward to perform braking, the seal 30 is deformed as shown in FIG. 2. When the braking pressure is released, the seal 30 returns in the direction opposite to arrow A to an original state thereof shown in FIG. 1. Accordingly, the piston 22 is moved back to an original position thereof by the resilience of the seal 30. This action is referred to as roll-back. The return distance of the piston 22 depends on the deformed width (L) of the seal 30.
However, in the conventional disc brake 10, since the side of the seal 30 facing the direction in which braking is performed is a flat surface roughly perpendicular to the outer surface of the piston 22 as shown in FIG. 1, and the deformed width (L) of the seal 30 is limited as shown in FIG. 2, and thus the return distance of the piston 22 may be short. That is, the deformation of the conventional seal 30 is small, and thus increasing the return distance of the piston 22 may be limited. If the return distance of the piston 22 is short, the friction pads 12 attached to the pad plates 11 may not be sufficiently separated from the disc when the braking pressure is released, resulting in wear of the friction pads 12. That is, high drag may be caused depending on the amount of roil-back given by the machining allowance of the cylinder 21 and the frictional force generated between the seal 30 and the piston 22.
Further, when the piston 22 returns to an original position thereof, the piston 22 may undergo knock-back, which refers to a phenomenon in which the piston 22 moves forward again by elastic force of the seal 30 after moving in the return direction. In addition, when the braking pressure is released, the caliper housing 20 slidably moved from the carrier returns to an original position thereof along with elastic return of the piston 22 by the seal 30. But when the caliper housing 20 is moved leftward in this process, the piston 22 may undergo back slip, that is, slipping in the direction of forward (leftward) movement of the piston 22, which is caused by the seal 30 installed at the roll-back chamfer.
Meanwhile, when a compression spring (not shown) is used to move the piston 22 backward, it is installed at the pad plate 11, which is pressed against the disc D, to provide elastic force in the direction opposite to that of pressing the pad plate 11 against the disc D.
However, when the compression spring is used, the amount of roll-back increases as the friction pad 12 is worn, resulting in poor initial braking feeling. Further, excessive roll-back of the piston 22 caused by the compression spring may cause a sinking brake pedal.